Acoustic device



J. Q. SAUBER-r Erm. Re. 22,017

- Acous'uc nEvicE original Filed," Jan. 5. 1931 Z M 1.. 3 F

' companying bodiment of one form of the *present invention Reuma Feb. 3, 1942 UNITED STATES" PATENT OFFICE- .lloous'rro DEVICE John Q. Ganbert, Yonkers, N. Y., and John D. Seabert, Collingswood, N. J.,A assignors, by

' mesne assignments, to Radio Corporation of America, -New York, N. Y., a corporation ol l Delaware original No. 1,991,738, dated February 19, 1935,

Serial No. 506,676, January 5, 1931. Applica.-

tion lor reissue September 11, 1936, Serial No.

18 Claims. `(Cl. 179-120) This invention relates to an acoustic device Y and more particularly to a dynamicspeaker having a permanent ileld magnet.

In'the use of loud speakers provided with a movable speech coil in connection with battery operated receivers, it is not practical to provide an electro-magnetic field for the movable speech coil. It has been proposed to use a cast cobalt steel magnetic field. vAs is Well known to those skilled in the art, a permanent magnet that is to be used in connection with a movable speech coil must be made to very accurate dimensions. The allowabletolerance in the air gap is oftentimes only of the order of a thousandth of an inch. This being the case, it is necessary to nish the cast piece by suitable tooling. This is not practical if the permanent magnet is made from such material as cobalt steel having great,

magnetic retentivity, for the reason that cobalt steel is too hard to be successfully tooled, especially in mass production.

An object of this invention is to provide a to cooper'ate with the nuts 32 and the lock washers 34, thus' securing the members 28, 2l and 22 to the supporting rim I8 of thehousing Il.

The small end 36 of the frustro-conical daphragm 26 is cemented or otherwise secured to the outer surface of, a flared rim 38 of a speech coil support 40 which carries a, movable speech coil 42. The two terminals 4I, only one o1' which is shown, are wound around a pair of conductors 46, and conductively secured thereto in any suitable manner as at 48. One end 50 of each conductor 4l projects through a hole 52 inside of the speech coil support 40 and is cemented or otherpermanent cobalt magnet that does not extend f near the air gap. Thishas been accomplished by providing a short magnetic piece ,of cobalt steel that may bepermanently magnetized and E that forms part of a magnetic circuit, the balance'oi which includes suitable ferro-magnetic material that may be easily tooled.

Another object oi this invention is to reduce ritlcing the elliciency of the magnet.

Further objects and advantages of the presu ent invention will be apparent from the following description, reference being had to the acrawing wherein a preferred emis clearly shown.

The drawing represents a cross section through a dynamic acoustic device which is 'provided with'a permanent held magnet.

Referring to the drawing, a cup shaped ileldf o! a sound damping felt cone and the flared portion 2l o! a sound reproducing cone or diaphragm 26 held in position by a clamping ring 2l. A plurality oi screws 30 extend through plain holes in members 2l, 2l, 22 and" so as net has been used which is made from tempered the cost, save material, reduce the labor re`l quired in the making of a magnet without sacwise secured thereto as at 5l. The other end of each conductor 46 is conductively fastened to one of a pair of terminals 56 that are connected to an external circuit (not shown).

'In the conventional electro-dynamic speaker, the center pole piece' is usually made from a piece of ferro-magneticv material that has one end riveted, welded or votherwise lsecured to a magnetic housing and the other. end machined so as' to accurately fit within a movable speech coil. This structure is very satisfactory where the Vmagnetic eld is :produced by a magnetic coil properly energized.

In the present modification a permanent magcobalt steel. Cobalt steel that has been tempered is very hard to mill or machine. 'I'his being the case. if it shall bemachined, it is necessary to4 machine cobalt steel before it istempered. I! this ls done, it is practically impossible to temper the cobalt steel after assembling.

In the modification disclosedinthe drawing. the center pole piece comprisves'two pieces, one a tempered cobalt steel cylindrical stud piece il and the other a cylindrical cap B4A of ferro-magnetic material. The stud piece 86 is seated in the recess Il in the magnetic housing I2 and held therein by means `of a plurality ofA screws 1l passing through a 'center brass annulus v1l provided With an aperture 12 that snugly fits around the machined portionv 6l of the other pole piece or cap 64 and that engages a shoulder 13 integral with an annular Iiange 10. The cap 6l ts around the center pole piece 66.

An annular pole piece 90 provided with a recess I8 is held in position by a flange 81 integral'with 86 that extends into therecess 88 and is held in relatively ilxed position by the screws 94 that pass through suitable holes in the annular pole piece and threadedly engage the brass annulus 14. Itcan bereadily seen that as the screws 94 and the nuts l0 are tightened, the annularpole piece 64 by the brass annulus 'I4 and that the cap 64 cooperates with the housing I2 to clamp the center pole piece 66 into position. The center lpole,

piece 66 having great magnetic virtue or retentivity upon beingproperly magnetized cooperates with the magnetic housing i2, the annular pole piece 90, the air gap 92, and the center pole piece cap 64 to form a magnetic path. l f

By this arrangement, the air gap 92 formed between the annular pole piece 90 and the. cap 64 is always uniform so that the movable speech coil 42 and its support 4!) can move axially without interference with the pole pieces.

While the form of embodiment of the present invention as herein disclosed, constitutes apreferred form, it li.s .r.to.;be understood that other forms mightbe'adopted, all coming within the'- scope of the claims which follow. yWhat is claimed is as follows: ,1. A permanent fleld magnet in a dynamic acoustic device, comprising in combination, a`

whereby the annular pole piece and the center pole piece 'are held in a relatively fixed relation with respect to said field housing.

6. As an article of manufacture, a permanen fleldmagnet comprising a cup-shaped field housing of ferro-magnetic material; an annular pole piece, a permanently magnetized center pole; a center pole piece cap of ferro-magnetic material; a centering member engaging said cap and said annular pole pieceand means for clamping the centering member to the eld housing so that the l annular pole piece, the center pole piece and the magnetic housing are held in a relatively fixed relation.

7. As an article of manufacture, a permanent field magnet, comprising, a field housing; a center pole cap having a shoulder; a clamping disc engaging said shoulder; and a plurality of adjustable fasteners cooperating with the field housing to clamp the .disc against said shoulder whereby the center 4pole piece and the field housing are held in a relatively fixed relation.

field housing, afpermanently magnetized center pole piece, an annular pole piece, a non-magnetic member for locating the annular pole piece with respect to the center pole piece, fastening means for securing thecenter polepiece in position, and means for securing the annular pole piece to the field housing through said locating member.

2. A permanent field magnet in a dynamic Y acoustic device, comprising in combinationf a` field housing, av permanently magnetized center pole,

3. A permanent field magnet in a dynamic acoustic device comprising in combination, a

field housing; a permanently magnetized center pole; an annular pole piece, interposed means for locating the center pole with respect to the annu- 8. As an article of manufacture, a permanent field magnet, comprising a field housing provided with a recess, a permanently magnetized pole piece, said pole piece being received by said recess; a center pole cap of magnetic material, provided with a recess for receiving the other end of the pole piece, a clamping member, said cap having a shoulder for cooperating with said clamping member, and a plurality of adjustable fasteners that supply the clamping pressure.

9. As an article of manufacture, a permanent field magnet,` comprising a field housing; a permanently magnetized cylindrical center pole; an annular pole piece surrounding the center pole, said annular pole piece having a groove; a centering member having a central annular aperture Acentering member having an -annular iiange engaging the groove in said .annular pole piece whereby the air gap is maintained fixed.

larpole piece; means vfor securing the locating means to the field housing thereby securing the centerpole in position, and means for securing the annular pole piece to said interposed locating means. l y

4.1A permanent field magnet in a dynamic acoustic device, comprising in combination; 'a a field housing; an annular pole piece; a permanently magnetized center pole piece, a ferromagnetic center polepiece cap, a non-ferro-magnetic member for locating the center pole piece cap within an aperture of the annular pole piece: fastening means for securing the center pole in position; and adjustable fastening means for securing the annular pole piece to said non-ferromagnetic member and to the eld housing.

5. A permanent field magnet in a dynamic acoustic device, comprising in combination; a field housing; a permanently magnetized center pole piece, an annular pole piece; a locating and clamping non-ferro-magnetic member for securing the center pole to the field housing; aplural-y ity of pressure supplying fasteners for the locating and clamping member; said locating and clamping member holding thevcenter pole within great magnetic retentivity whereby it may bev an aperturejof the annular pole piece, and a plurality of adjustable fasteners for securing the annulai" pole piece to said combined locating and r clamping member and lto the field housing,

10. As an article of manufacture, a permanent eld magnet, comprising a field housing, a permanently magnetized center pole having a vfinished Vcylindrical portion, an annular pole piece having an annular groove, said groove being concentric With respect to said cylindrical portion;

a centering disc which has a central annular and adjustable fastening means for securing the annular pole piece to the centering d isc.

1 1.. As fan article of manufacture, a permanent field magnet, comprising a field housing; a permanently magnetized center pole having a cylin-v drical portion; an annular pole piece having an annular groove; a disc member having a depending central annular rim that projects into said annular groove, and a plurality of screws for securing the annular pole piece to the disc member.

12.1A permanent field magnet comprising, in combination, a iield housing; a center pole piece; an `annular lpole piece, said annular pole piece having a groove, one of said pole pieces'having permanently magnetized, a cap for said center pole piece, said cap having ,a shoulder; a centering disc having a cylindrical recess engaging the shoulder, a projection on said disc engaging said groove and fastenersengaging said annular pole piece and said housing, said fasteners holding the piece cap in a fixed relation.

13. A permanent field magnet, comprising in combination, a field housing, a center pole piece, an annular pole piece having a groove, one of said pole pieces having great magnetic retentivity whereby it may be permanently magnetized, a cap for said center pole piece, said cap having a. shoulder, a centering disc having a cylindrical recess engaging the shoulder, a projection on said disc engaging said groove, and means securing the annular pole piece to the field housing there-` by securing said centering disc in position.

14. A permanent field magnet, comprising incombination, a field housing of ferromagnetic material, a permanently magnetized center pole piece, an annular pole piece having an annular groove, a cap of ferromagnetic material for said center pole piece,l a 'centering disc of non-ferromagnetic material fitting over the periphery of said cap, said disc also having a depending annular rim projecting into the annular groove of said annular pole piece, and means securing the annular pole piece to the field housing thereby securing said centering disc in position.

15. A permanent field magnet, comprising in` combination, a field housing of ferromagnetic material, a permanently magnetized center pole also having a depending annular rim adapted to' piece, an annular pole piece having an annular Y groove, a cap of ferromagnetic material for'said center pole piece, said cap having a flanged portion, a centering discof non-ferromagnetic material fitting over the periphery of said cap and resting against the flanged portion thereof, said centering disc also having a depending annular rim adapted to project into the annular groove of the annular pole piece, and means securing the annular pole piece to the field housing thereby maintaining said centering disc interposed between the flanged portion of the cap and the annular groove ofthe annular pole piece.

16. A permanent field magnet, comprising in combination, a field housing of ferromagnetic material, said housing having a recess, a cap of ferromagnetic material having a recess similar to that of the field housing and a flanged portion, a permanently magnetized center pole piece interposed between said field housing and said cap and located within the recesses thereof, a center. ing disc of non-ferromagnetic material fitting over the periphery of said cap' and resting against the flanged portion thereof, said centering disc project into the annular groove of the annular pole piece, and means securing the annular piece to the field housing thereby maintaining said centering disc interposed between the flanged portion of the cap and the annular groove of the annular pole piece and also maintaining said center pole piece located within the recesses of the field housing and the cap. u

17. A magnet system for dynamic acoustic apparatus comprising a central pole piece, an'outer pole piece, a spacing member having an opening therein within which said central pole piece fits, an upturned portion on said spacing member, a recess in said outer pole piece in which said up-turned portion is movable inwardly and outwardly in adjusting thespacing between the spacing member and the outer pole piece, and screw means extending between said outer pole piece and said spacing' member for drawing saidk spacing member toward said outer p'ole piece the desired amount.

18. A magnet system for dynamic acoustic apparatus comprising a back plate, a central pole piece, a member forming an outer pole piece, a shoulder yonsaid central pole piece, a member fitted aroundsaid pole piece and engaging said shoulder for exerting a pressure against said shoulder in the direction to -force said central pole piece towards said back plate, and means extending between said back plate and one of said members for drawing said member towards said back plate, whereby said central pole piece` is held against said back plate.

JOHN Q. GAUBERT. JOHN D. SEABERT. 

